Crystalline aluminosilicate zeolites dispersed into a matrix of amorphous and/or amorphous/kaolin materials have been employed in the catalytic cracking of hydrocarbons for many years. The poisonous effects of metals contained in the feedstock when, for example, a gas oil is converted to a gasoline range boiling fraction, in lowering catalyst activity and selectivity for gasoline production and in reducing catalyst life have been described in the literature.
Initially, these adverse effects were avoided or controlled by charging feedstocks boiling below about 1050.degree. F. and having total metal concentrations below 1 ppm. As the need for charging heavier feedstocks having higher concentrations of metals increased, additives such as antimony, tin and barium have been employed to mitigate the poisonous effects of metal contaminants such as nickel, vanadium and iron contained in the catalytic cracking process feedstocks. Reference is made to U.S. Pat. Nos. 3,711,422; 3,977,963; 4,101,417; and 4,377,494 as illustrative of such passivation procedures.
Recently, it had been disclosed that hydrocarbons containing vanadium can be converted to lower boiling fractions employing a zeolitic cracking catalyst containing a significant concentration of a calcium-containing additive as a vanadium passivating agent (U.S. Pat. No. 4,520,120) or by employing a catalytic cracking composition comprising a solid cracking catalyst and a diluent containing selected magnesium compounds as a vanadium passivating agent (U.S. Pat. No.4,465,589).